The objective of the proposed research is to establish causal relationships that exist among neuroendocrine, neural and endocrine factors in the regulation of prolactin secretion in males. Using a rat animal model, experiments test whether the male's central nervous system can elicit specific endocrine and neuroendocrine responses to the presentation of young, i.e., a suckling challenge. The effects of steroid-priming and behavioral inputs on plasma prolactin and luteinizing hormone concentrations are measured by radioimmunoassay and the results between males and females compared. The ability of parental behavior to alter hypothalamic sensitivity and neurotransmitter activity (serotonin, dopamine) is examined and possible sex differences evaluated. Finally, the effects of androgen exposure during prenatal and postnatal development on the ability of the animal to process peripheral and central information relating to the animal's behavioral-endocrine state are examined to determine possible "organizational" effects of hormones on hypothalamic function, i.e. the suckling center. These results should provide new information regarding neuroendocrine function in the male and a further understanding of factors that control prolactin secretion in mammals.